The techniques of lubricant feed mechanisms for turbochargers that feed lubricant to a bearing part that rotatably supports a shaft connecting a compressor wheel and a turbine wheel have hitherto been known. For example, the technique is described in Patent Literature 1.
Patent Literature 1 describes a lubricant feed mechanism 901 for a turbocharger 905 as shown in FIG. 6. In this lubricant feed mechanism 901, lubricant stored in an oil pan 902 is fed to a bearing housing 940 of the turbocharger 905 by an oil pump 904 via a forced feed oil passage 903.
The lubricant fed to the bearing housing 940 is guided to a bearing part 941 that rotatably supports a shaft 910 connecting a compressor wheel 920 and a turbine wheel 930 to lubricate the bearing part 941. After lubricating the bearing part 941, the lubricant is returned to the oil pan 902 via a return oil passage 906.
In this lubricant feed mechanism 901, a throttle 951 is provided in the forced feed oil passage 903. Further provided is a drain oil passage 907 that connects the forced feed oil passage 903 (more particularly, the upstream side of the throttle 951 in the forced feed oil passage 903) and the return oil passage 906 so as to bypass the bearing housing 940, and a pressure adjusting valve 952 is provided in this drain oil passage 907.
In the lubricant feed mechanism 901 configured as described above, the throttle 951 ensures that a minimum necessary amount of lubricant is fed to the bearing part 941, and the pressure adjusting valve 952 prevents an excessive supply of lubricant to the bearing part 941. Specifically, when the discharge pressure of the oil pump 904 rises (and in turn the pressure in the forced feed oil passage 903 rises), the pressure adjusting valve 952 opens to release the lubricant in the forced feed oil passage 903 into the drain oil passage 907, whereby the pressure in the forced feed oil passage 903 is adjusted not to exceed a predetermined level. In this way, the lubricant can be prevented from being fed excessively to the bearing housing 940.
One disadvantage of such a lubricant feed mechanism 901 is that some amount of work done by the oil pump 904 is wasted because the oil pump 904 feeds a large amount of lubricant under pressure that includes not only the lubricant to be fed to the bearing housing 940 but also the lubricant that is to be released via the pressure adjusting valve 952.